Vibration generators of such kind can be employed in a variety of applications, for instance in such applications where loose goods are to be compacted, e.g. in the packaging industry or in the production and compaction of cast pieces made of concrete or similar material. Likewise, there is a wide range of applications given in foundation construction engineering for producing boreholes in the soil or for soil compaction.
In devices employed for soil compaction two rotating unbalanced mass elements are arranged alongside each other. One unbalanced mass element is connected to a drive unit, while the second one is driven by a gear. The phase position of the unbalanced masses on the respective unbalanced shafts can be adjusted so that a feed motion of a vibrating plate is infinitely adjustable.
DE 195 23 030 C2 discloses a vibrator having a housing, in which a movably supported excitant for generating vibrations and a drive for the excitant consisting of a piston-cylinder unit are arranged. The excitant is rigidly coupled with a hydraulically driven drive piston of the piston-cylinder unit and is reciprocable in a linear fashion with respect to the action of spring and damping means that are variably adjustable in their spring characteristic.
There are also vibrators known that are operated by a pressure medium.
DT 24 45 215 A1 describes a vibrator comprising a piston seated in a displaceable manner in a cylinder, which has an inlet port and two outlet ports located in the wall of the cylinder. The cylinder or the piston are sleeved, and the sleeve forms cooling ducts for the passage of driving medium.
DE 39 15 773 A1 discloses a piston vibrator consisting of a case having a cylindrical bore, an air connection guided laterally to the bore and a piston that is longitudinally displaceable in the bore. At the axial level of the air connection the cylindrical bore extends asymmetrically to the external wall area of the case.
From DE 17 68 865 U1 a vibration generator is known, in which a drive piston is reciprocated mechanically at a constant amplitude in a housing. By means of an air column the drive piston, functioning as excitant, transmits a vibrating movement to a working piston that is freely movable in the same cylindrical housing and is coupled through an air column with the drive piston. On the side of the working piston lying opposite the air column a further air column is provided, with the volume of the two air columns being adjustable so that the vibrations of the working piston and its amplitude can be adjusted infinitely by means of the air volume of the air columns.
However, with air and other compressible media it is very often not possible to achieve sufficiently high power levels. For this reason it is necessary to render vibration generators more efficient whilst having the same external dimensions or to make them more compact whilst retaining the same power. This can be achieved e.g. by using incompressible media as working fluid. However, in such cases very high demands are often made on the complexity of the construction.